The invention relates to the field of Chemical Mechanical Planarization (CMP).
Other than global planarization and high polish rate, the Chemical Mechanical Planarization (CMP) process should also achieve high material selectivity (high polishing rate of one material compared to the other), high quality surface finish, which is devoid of scratches, pattern related defects, pits and particle contamination.
The CMP process synergistically combines both tribological and chemical effects to planarize metal like copper, tungsten and insulating materials such as silica and polymers. FIG. 1 shows the schematic diagram for the CMP process. The polishing process involves active abrasion of the wafer surfaces using abrasive particles present in the slurry and active mechanical component, provided by the polishing pad. Such an abrasion results in surface scratches on the surface of the wafer. The scratches result in formation of puddles in further layers causing an electrical short circuit. As the industry progresses into the 45 nm node and beyond, the requirement for post CMP surface quality and defects becomes more critical. Oxide CMP is conducted during shallow trench isolation in logic device fabrication and also in many other novel applications. Defects during CMP hamper the device yield and reducing the defects is thus highly important. These defects result in nullifying the advantages of using CMP as a global planarization technique.
CMP defects arise due to contamination issues from slurry chemicals, particle contamination (residue) from abrasive, scratches during polishing due to agglomerated abrasive particles, pattern related defects like dishing and erosion, delamination and dielectric crushing due to mechanical damage of dielectrics. Therefore, what is needed is a novel slurry for use with the CMP process containing soft particles that do not cause as aggressive scratching, leave particle residue, or apply high mechanical stress.
Composite materials containing polymeric and inorganic units have been attracting considerable attention in the areas of medicine, paint, and specialty chemical industries. For example, polymer-inorganic oxide composites are promising candidates as slurries for chemical mechanical polishing while zinc oxide particles coated with fluoropolymers are an important constituent of cosmetic foundation creams. Composites of poly(vinyl alcohol)-TiO2 are being examined as a cheap replacement for nafion-platinum membranes for application in alkaline direct methanol fuel cells.
To obtain polymer-inorganic microcomposites, a few researchers have explored using supercritical fluids as a means to incorporate insoluble inorganic nanoparticles into the organic network. One drawback lies in that these nanoparticles often aggregate within the polymer thereby reducing the effective surface area. Other approaches have involved using polymer synthesized by emulsion polymerization to encapsulate inorganic or metallic nanoparticles. However the organic-aqueous interface required for polymerization frequently requires toxic organic solvents, surfactants, and stabilizers that can be difficult to remove and can create environmental problems. Therefore, approaches using polymers that do not require organic solvents or stabilizers and that are easy to load with nanoparticles to create composites can be quite useful.
In recent years the fabrication of stimuli responsive polymeric materials based on N-isopropylacrylamide has generated much interest due to its ease of synthesis in aqueous media and their technological application. These stimuli responsive polymers can respond in shape and size to external stimuli like temperature, pH, ionic strength, etc. PNIPAM is a nonionic polymer typically, prepared by free radical precipitation polymerization. In aqueous solutions, PNIPAM displays a reversible phase transition behavior around an easily accessible temperature of 32° C. As a result, PNIPAM has become the most widely studied water based temperature sensitive polymer. Since the first synthesis of poly(N-isopropylacrylamide) (PNIPAM) microgels by Pelton in 1986, cross-linked, microspherical particles or “microgels” of PNIPAM have been of particular interest. These microgels are typically achieved using a divinyl compound to cross-link the polymer chains into a porous network.